Lecithin cholesterol acyltransferase (LCAT), the major enzyme which esterifies cholesterol present in plasma lipoproteins, plays a central role in HDL metabolism. Patients with LCAT deficiency may present with corneal opacities, anemia and renal disease as well as reduced plasma HDL-C and apoA-I concentrations. To evaluate the role that LCAT plays in reverse cholesterol transport and the development of atherosclerosis we have established a mouse model for human LCAT-deficiency by performing targeted disruption of the LCAT gene in mouse ES cells and crossed the LCAT-KO mice with CETP-Tg, apoE-KO and LDLr-KO mice. On a high fat/high cholesterol (HF/HC) diet, cholesterol (-55%), HDL-C (-94%), apoAI (-83%) and apoB-lps (-48%) were decreased in LCAT-KO vs. cholesterol (p<0.01, all). Similar decrease in plasma lipids were found in LCAT-KO mice crossed with either CETP-Tg, LDLr-KO, or apoE-KO mice. Cathodally migrating LpX containing albumin and apoCs were present in 62% of LCAT-KO mice on the HF/HC diet. Only LCAT-KO mice on the HF-HC diet with LpX developed proteinuria and renal lesions, with mesangial proliferation/sclerosis, deposition of electron dense material by EM, polar lipids and free cholesterol, by Oil-red-O and Filipin staining. Compared to cholesterol, LCAT-KO mice had normochromic normocytic anemia, reticulocytosis, increased target cells, and decreased RBC osmotic fragility. LCAT-def decreased diet induced aortic atherosclerosis (mm2) in LCAT-KO (1022+/-325) vs. control (5066+/11031; p<0.01) and abolished atherosclerosis in LCAT-KO x CETP-Tg (0+/-0) vs. CETP-Tg (10100+/-1800; p<0.001). LCAT-def decrease spontaneous atherosclerosis in apoE-KO mice (LCAT-KO x apoE-KO 19200+/-7600 vs. apoE-KO 66700+/-15500; p<0.05). Analysis of hepatic mRNA expression by Affimetrix chip hybridization revealed increased transcript levels of apoE (2x) and LDLr (4x) in LCAT-KO vs. cholesterol with no changes in SRBI, LRP, apoB, HL, ABC1 and ABC8. Summary: 1) LCAT-KO mice are an ideal model for FLD with decreased HDL, anemia and renal disease; 2) The association of LpX with the development of renal disease substantiates an etiological role for LpX in glomerulosclerosis; 3) LCAT-def decrease plasma apoB-lps as well as HDL and decrease atherosclerosis in C57Bl, CETP-Tg and apoE-KO mice; 4) Oligonucleotide chip analysis indicates that LCAT-def increase LDLr expression resulting in decreased plasma apoB-lps; and 5) These combined data provide new insights into mechanisms by which LCAT modulates lipoprotein metabolism and atherosclerosis.